Various medial imaging systems and apparatus provide the desired imaging according to phenomenon associated with the tissue. For instance, the absorption of x-rays is exploited for x-ray and computer-aided tomography imaging. The effects on nuclear spin of various molecular elements is used in the nuclear magnetic resonance (NMR) imaging systems. Ultrasonic imaging is provided by exploiting the reflectance and transmissivity of the tissue. All imaging systems have particular limitations and features for their applications. However, one such limitation of imaging systems are that they are generally tissue-selective, whereupon only a few types of tissue features provide a varying phenomenon measurable by the particular imaging system necessary to produce the desired image.
Of particular interest in the practice of oncology is observation of the development of new capillaries at tumor sites. However, many of the available imaging techniques fail to provide the desirable information necessary to provide a useful image. Alternatively, invasive techniques such as injecting an radioactive opaque dye produce an image, but also produce discomfort to the subject and create a degree of risk. It is therefore useful and important to the medical community to provide high-contrast imaging of the circulatory system with minimal patient discomfort and risk.
In addition to NMR imaging, other prior art measurements of body tissue in a magnetic field presume that the body tissue acts a attenuator of the field. However, the attenuation provided by such models only provides one part in 10.sup.-5 attenuation, providing a change in magnetic field which is well into the noise and experimental error of such apparatus. The signal is insufficient to provide the information to create useful results, let alone tissue imaging.